Computer-aided detection and enhancement of microcalcifications in mammogram images is described by Gürcan et. al. in “Automated Detection and Enhancement of Microcalcifications in Mammograms Using Nonlinear Subband Decomposition,” Icassp, vol. 4, pp. 3069, 1997 IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP'97)-Volume 4, 1997.
Also in US patent application 2005/0135695 a similar approach is described.
The general idea of the described method is a 3-step process to create an enhanced mammogram image: 1. detection of microcalcifications in the image, 2. segmentation of the microcalcifications in the image and 3. enhancing the microcalcifications in an image.
The prior art proposes two approaches to create an enhanced version of the mammogram: the amplification technique and the superposition technique.
In the amplification technique the pixel values of the original image are amplified by an amplification factor at the locations of microcalcifications which are provided e.g. by a computer aided detection system. The amplification factor can be fixed or may depend on the characteristics of the segmented microcalcification and its surrounding tissue.
In the superposition technique segmented microcalcifications are superimposed on the original mammogram image at the locations of the microcalcifications.
For both techniques the enhancement of the microcalcifications in the processed result image strongly depends on the accuracy of the segmentation of the individual microcalcifications. This can lead to abrupt transitions and an artificial enhancement at the boundaries of the segmented regions. Image enhancement based on an inaccurate segmentation can possibly change the shape of the microcalcifications.
An accurate delineation of microcalcifications in a mammogram image is difficult, especially in a mammogram generated with computed radiography technology because of the poor contrast-to-noise ratio of the microcalcifications in the image.
Another technique to optimize the visualization in a subsection of a mammogram image is used by Heinlein et. al. in US patent application 2009/0174727, entitled “Method and apparatus for improved display of digital mammographic images”.
The idea described in this patent application is to optimize the contrast in a subsection of the image by applying a spreading function to the range of values of the pixels in the subsection and by decreasing the contrast optimization towards the boundary of the subsection by applying a weighing function in order to create a gradual transition of the contrast between the subsection and the rest of the image.